Question

High-strength concrete is supposed to have a compressive strength greater than 6,000 pounds per square inch (psi). A certain type of concrete has a mean compressive strength of 7,000 psi, but due to variability in the mixing process it has a standard deviation of 420 psi. Assume a normal distribution. What is the probability that a given pour of concrete from this mixture will fail to meet the high-strength criterion? In your judgment, does this mixture provide an adequate margin of safety?